Low birth weight

A low-birth-weight baby is defined as a child weighing less than 5 and a half pounds at birth. This is commonly associated with premature delivery, but other factors are known to cause it as well, such as maternal smoking, exposure to lead, or some prenatal infections. Low birth weight can cause a variety of complications, including lifelong, chronic health problems and possibly neonatal death.

No cause and effect proven

Researchers studied over three million births in North America, South America, Europe, Asia and Australia. They found that where there was more smog, there was more of an incidence of low birth weight.

"They found that where there was more smog, there was more of an incidence of low birth weight"

Study authors say that despite the findings that do show an association, there is no absolute cause-and-effect relationship proven. "What's significant is that these are air-pollution levels to which practically everyone in the world is commonly exposed," study co-principal investigator Tracey Woodruff, a professor of obstetrics and gynecology and reproductive sciences at the University of California, San Francisco, said in a university news release. "These microscopic particles, which are smaller than the width of a human hair, are in the air that we all breathe."

Tighter regulation pays off

Areas with tighter regulations of on this type of air pollution happily do show lower levels, so regulations do work. Authors note that in the US, these results reflect other studies that have been done on air pollution, and how the benefit to human lives is well worth the cost for regulating and reducing smog.

Study co-author Mark Nieuwenhuijsen, of the Centre for Research in Environmental Epidemiology in Spain, said in the news release: "This study comes at the right time to bring the issue to the attention of policy makers."